Question

Why on the first line of class actionPerformed(), can I not use the protected JMenuItem menuItem; variable which I declared at the top of the MainMenuBar() class?

The 2nd line is the one I commented out, and it works.

But, I want to be able to use one JMenuItem object name across classes without having to reinstantiate it.

How can I reuse menuItem here correctly?

Thank you.

package base;

import javax.swing.JMenuBar;
import javax.swing.JMenu;
import javax.swing.JMenuItem;
import javax.swing.JTextArea;

import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import java.awt.event.KeyEvent;

public class MainMenuBar implements ActionListener {
    protected JMenuBar menuBar;
    protected JMenu menu;
    protected JMenuItem menuItem;

    JTextArea output;
    String newline = "\n";

    public JMenuBar getMenuBar() {
        menuBar = new JMenuBar();

        // 1st Menu
        menu = new JMenu("File");
        menu.setMnemonic(KeyEvent.VK_F);

        menuItem = new JMenuItem("New Note");
        menuItem.setMnemonic(KeyEvent.VK_N);

        menu.add(menuItem);
        menu.addSeparator();

        menuItem = new JMenuItem("Exit");
        menuItem.setMnemonic(KeyEvent.VK_X);

        menu.addActionListener(this);
        menu.add(menuItem);

        menuBar.add(menu);

        // 2nd Menu
        menu = new JMenu("Help");
        menu.setMnemonic(KeyEvent.VK_H);

        menuItem = new JMenuItem("About Java Sticky Notes");
        menuItem.setMnemonic(KeyEvent.VK_A);

        menu.addActionListener(this);
        menu.add(menuItem);

        menuBar.add(menu);

        return menuBar;
    }

    @Override
    public void actionPerformed(ActionEvent e) {
        menuItem source = new JMenuItem("MainMenuBar.java");
        //JMenuItem source = (JMenuItem) (e.getSource());
        String s = "Action event detected." + newline + "    Event source: "
                + source.getText() + " (an instance of " + getClassName(source)
                + ")";
        output.append(s + newline);
        output.setCaretPosition(output.getDocument().getLength());
    }

    // Returns just the class name -- no package info.
    protected String getClassName(Object o) {
        String classString = o.getClass().getName();
        int dotIndex = classString.lastIndexOf(".");
        return classString.substring(dotIndex + 1);
    }
}

Answer 1

You have a syntax error, compiler assumes menuItem is a class, since it is followed by source. Change the following:

menuItem source = new JMenuItem("MainMenuBar.java");

to:

menuItem = new JMenuItem("MainMenuBar.java");

But then you have to take care of the source, since it is used in the following lines.